Fibers



June 14, 1966 A. J. HERRMAN 3,256,258

FIBERS 4 Sheets-Sheet 1 Filed May 5. 1961 FIG. FIG.2

INVENTOR ARTHUR JOHN HERRMAN Y *MLQQLVL.

ATTORNEY June 14, 1966 A. J. HERRMAN FIBERS 4 Sheets-Sheet 2 9 zizaziu 8mdzl ICSINVENTOR ARTHUR JOHN HERRMAN HJINQG ISHVHS BY ),.W-

ATTORNEY June 14, 1966 J, HERRMAN 3,2565258 FIBERS 4 Sheets-Sheet 5Filed May 5. 1961 FIG. 4

so so ELONGATION,

o' Hum ARTHUR JOHN HERRMAN BY w- ATTORNEY June 14, 1966 A. J. HERRMANFIBERS 4 Sheets-Sheet 4 Filed May 5, 1961 EOUATOR FIG.6

INVENTOR ARTHUR JOHN HERRMAN ATTORNEY United States Patent O 3,256,258FIBERS Arthur John Herrman, Wilmington, Del., assignor to E. I. du Pontde Nemours and Company, Wilmington, DeL, a corporation of Delaware FiledMay 5, 1961, Ser. No. 108,001 4 Claims. ((31. 260-937) This inventionrelates to fibers and, more particularly, to elastomeric fibers ofpolypropylene.

Much effort has been expended heretofore in attempting to make fibersfrom synthetic polymers having many of the desirable attributes offibers made from natural rubber without the disadvantages of naturalrubber fibers. Results have been varied but, on the whole, theseattempts have not been too successful. Usually, fibers have hadextremely low moduli of elasticity in the regions of the elongation usedin most applications of fibers. That is, the fibers were characterizedby a very low stress at useful elongations and, hence, required heavydenier fibers to provide suitable resistance to elongation. The problemof getting a fiber with, in laymans language, some elasticity but not aruinous amount, persisted.

Not only have the heretofore proposed polymers been lacking in desireddegree of elasticity when formed into fibers but the solutions proposedhave involved polymers whose production was quite expensive anddifficult to control.

Fibers from highly crystalline, high molecular weight polypropylene arewell known. Although some of these fibers have ben described as highlyelastic, useful elastic fibers of propylene have nevertheless not beenforthcoming and, in general, the problem of producing useful elasticpolypropylene fibers and the like has been just as difficult as whenusing other synthetic polymers.

An object of this invention is to provide new fibers of polypropylene. Afurther object is to provide such fibers having a suitable balancebetween elasticity, i.e., recovery [from elongation, and a useful degreeof resistance to elongation. A more particular object is to providefibers of polypropylene adapted for a wide variety of uses in which somedegree of elasticity is highly desirable, such as auto seat covers,covers for lawn chairs, carpets, and hose. Other objects will beapparent from the description of this invention given hereafter.

The above objects are accomplished according to the present invention byforming fibers of polypropylene whose physical structure ischaracterized by gamma orientation and a heat-stable orientation angleof 10 to 30. In a preferred form, the invention comprises a fiber ofpolypropylene having a gamma intensity ratio of at least 1.0 and aheat-stable orientation angle of 10 to 21".

It has been found that fibers of polypropylene whose physical structureis characterized by gamma orientation and a heat-stable orientationangle of 10 to 30 possess a highly favorable combination of properties,including good recovery from elongation. Such fibers have the followingproperties: a tenacity of at least 0.8 grams per denier, an elongationat break of from 100% to 700%, a tensile recovery on the second and thesucceeding cycles from a 25% elongation of at least 82%, a complianceratio (5% to 30% elongation) of from 2 to 15, a stress at 5% elongationof between 0.1 and 0.8 grams per denier, and an initial modulus of 5 toabout 25 grams per denier.

In the preferred form of this invention wherein the fiber ofpolypropylene has gamma orientation, a gamma intensity ratio of at least1.0, and-a heat-stable orientation angle of to 21, the fiber has atensile recovery on the second and succeeding cycles from a 25%elongation of at least 85% and, as shown in the examples, may be above90%.

"ice

For purposes of clarity and definiteness, certain terms used indescribing the invention are defined below. They are used throughout thespecification and claims as defined.

Orientation angle is a parameter which represents the alignment ofmolecular axes of the material forming a fiber with respect to the fiberaxis. The orientation angle is indicated by the azimuthal extent of theintensity of the (040) X-ray diffraction are at 20=16.7. These indicesare used according to G. Natta et al., Atti accad. nazl. Lincei, Rend.Classe si. fis. mat. e nat. [8] 21, 365 (1956). The orientation anglesare measured according to the technique by H. G. Ingersol, Journal ofApplied Physics, 17, 924 (1946), on the instrument described by J. E.Owens and W. O. Statton, Acta Crystallographica, 10, 560 (1957). Thisangle using the (040) are is a measure of crystallite orientation withrespect to the fiber axis (C axis).

Gamma orientation is the unusual orientation or condition of material inan object which is detected by X-ray diffraction techniques by adiffraction pattern in which the diffraction are at 26=14.0 exhibitsintensity maxima at an azimuthal angle greater than 50 from the equator.The intensity maxima has a ratio greater than 0.6 when compared to theintensity maxima of the (022, 122) X-ray ditfraction are at 20:28.6.This ratio (I'y/Iot), is determined from a radial photometer traceobtained 10 from the meridian on the Leeds and Northrup Knorr-Albermodel 6700-P-l microphotometer with 0.01 mm. slit width and 1.5 mm. slitlength. The peak intensities of the maxima are determined above thebackground scattering in the following manner: For the peak at 20:14.0"a straight line is drawn on the photometer trace connecting theintensity values at 26:93 and 20=ll.3; this sloping straight line isextended. under the peak and the intensity value of this line at thepeak 20 position is used as the background value and subtracted from thepeak value to give a quantity, 1 For the peak at 20=28.6 a slopingstraight line is drawn connecting the intensity values at 26:26.0 and312; the value on this line at the peak position is subtracted from thepeak value to give a quantity, Ia.

Oriented fibers having a gamma intensity ratio (I'y/Ia) of less than 0.6are designated as having normal orientation hereinafter. Oriented fibershaving a gamma intensity ratio greater than 1.0 are preferred.

By the term potential gamma orientation is meant a structure that willshow gamma orientation upon drawing to 1 to 2.5x and heating 10 minutesat C.

By the term heat-stable, used in connection with polypropylene in thegamma condition, is meant that the orientation angle does not changemore than 8% upon heating at a temperature of 135 C. for 10 minutes.

By the term tensile recovery which is hereafter designated TR, is meantthe percent of the elongation a fiber recovers after an elongation(stated as a subscript to the TR designation) at a rate of 100% perminute, being held at the maximum elongation for 1 minute and then beingpermitted to recover at the rate of 100% elongation per minute. Unlessotherwise designated, the 'TRs used herein to describe the invention areobtained from the second cycle on a tester 1 minute following therecovery from the first test after reclamping the fibers.

By compliance ratio, hereafter designated CR, is meant(compliance at 30%elongation-compliance at 5% elongation)/ 5 which may be expressed as Cao 5) 5 Where L and L ar the stress in grams per denier at therespective elongations. It will be noted that a high com- =2 plianceratio tends to indicate a fiber relatively easy to elongate 30% butrequiring almost as much effort to elongate %a rubber band would be anextreme illus tration. On the other hand, a low compliance ratio tendsto indicate a fiber relatively difiicult to elongate 30% butsubstantially easier to elongate 5%.

Initial modulus, hereafter designated Mi, is obtained by a straight lineextrapolation of the initial portion of the stress strain curve from 0elongation to 100% elongation. It is expressed in grams per denier,hereafter designated g.p.d. Tenacities and elongations at the break areexpressed in the usual units of g.p.d. and percent, respectively, andare measured on dry samples of yarns.

Polypropylene adapted for use in making the fibers of this invention, ishighly crystalline as shown by sharp and distinct X-ray diffractionpatterns and should preferably show a stiffness of greater than 120,000pounds per square inch when prepared in test bars according to ASTM testD-747. The polypropylene can be of any high molecular weight polymercharacterized by a melt index (ASTM standards, 1958 D1238-57T, part 9,page 38) of 0.1 to 200, preferably 0.5 to 30. The preferred rangeaffords products with significantly superior elastic properties.

The term inherent viscosity as used in the examples is defined as:ln(n),/c wherein c is the concentration in grams (0.10) ofthe polymer in100 ml. of the solvent (decahydronaphthalene), (n) is .the relativeviscosity which is the ratio of the flow times in a visoosimeter ofpolymer solution and of the solvent, both at 130 C. An antioxidant(0.2%) is normally added to both the polymer solution and the solvent.

The present invention resides in fibers of polypropylene as hereincharacterized and not in any particular method of preparing such fibers.However, preparation of the fibers does, in general, involveconsideration of three critical areas which are discussed belowspecifically in terms of fibers for purposes of simplicity and clarity.

1. Spinning c0nditi0ns.The extrusion of the fibers should be'under suchconditions so as to afford gamma orientation or potential gammaorientation. The spinning variables are adjusted to regulate theviscosity of the polymer melt as extruded through the spinneret hole,and the viscosity of the fiber as it changes from the molten to thesolid state in the threadline. Under any one set of conditions ofpolymer type, spinneret orifice dimensions, the number of orifices andpolymer throughput, gamma or potential gamma orientation is achievedthrough temperature regulation and windup speed. The temperature will bea function of the temperature of the molten polymer before beingextruded, the rate of extrusion, the geometry of the spinneret, theextent of cooling or heating on the spinneret by outside heat orquenching air. A cooling air quench may be used as the fibers form toassist with the proper temperature control.

2. Orientati0n.The fiber should be oriented to an extent giving anorientation angle of to'55 by suitable selection of spin stretchingunder suitable quenching conditions (i.e., windup speed/calculated speedof polymer leaving the orifice) and/ or suitable drawing of thesolidified fiber. The drawing can be done under any suitable conditionsbut the draw ratio must not exceed 2.5 X. Preferred products are madewithout drawing.

3. Heat treatment.This step is essential to the development of usefulrecoveries from tensional deformations in polypropylene. With fibersprepared under optimum spinning conditions (so that no separate drawingstep is needed) a temperature of 105 to 160 C. can be used for usefulproducts. For the best products, a temperature of from 130 to 140 C.should be used.

This treatment on fibers having gamma orientation produces a heat-stableorientation angle of 10 to 30, providing the fiber has an orientationangle between 10 and 55 before the heat treatment.

The fiber preferably is in a free-to-shrink condition dur ing thetreatment, the amount of relaxation (shrinkage) by the treatment usuallyvarying from 1 to 50%.

The time of treatment is not critical and can range from 0.6 second to24 hours. The heating can be done as a distinct separate process as inan oven or an autoclave or it can be conducted continuously.

The following examples illustrate specific embodiments of the invention.Reference is made to the accompanying drawings wherein:

FIG. 1 is a schematic showing of a fiber spinning and treating apparatussuitable for producing the fibers of this invention;

FIG. 2 is an enlarged side elevation of a spinneret and quenchingapparatus suitable for producing the fibers of this invention, shownpartly in vertical section for purposes of illustration;

FIG. 2a is a section on the line 2a2a of FIG. 2;

FIG. 3 illustrates stress-strain curves for various fibers of ExamplesI, II and III;

FIG. 4 illustrates two stress-strain curves showing the difierence inbehavior of a fiber in the first and second cycles on a tensile recoverytester;

FIG. 5 is a graphic representation of an X-ray diffraction photographillustrating gamma-type orientation which characterizes thepolypropylene of which the shaped articles of this invention arecomposed;

FIG. 6 is a graphic representation of an X-ray diffraction photographillustrating the normal orientation characteristic of the polypropylenein heretofore known shaped articles.

EXAMPLE I Crystalline polypropylene of melt index 0.7 (inherentviscosity of 2.75) (Profax made by the Hercules Powder Co., Wilmington,Delaware) is extruded as a melt at 289 C. through a spinneret 9 at 238C. (spinneret temperature measured at the surface) using the apparatusof FIG. 1 wherein the solidified yarn is advanced over the feed rolls 3and 4 rotating at 45 yards per minute (y.p.m.) then over the draw rolls5 and 6 rotating at the same speed, and is finally wound up on a package7. The spinneret 9 contains 34 orifices of 0.015 inch in diameterarranged in a rectangle one inch by 7 inch in a staggered disposition.As indicated generally by A in FIG. 1 and shown in detail in FIGS. 2 and2a, a quenching apparatus is disposed perpendicularly to the face of thespinneret 9. The quenching apparatus comprises a inch outside diametertube 10 containing a plurality of inch diameter holes adapted to directair against the walls of cylindrical chamber 11 in which it is mounted,except the wall facing the threadline. On the wall facing thethreadline, the chamber 11 is provided with a ZOO-mesh screen 12. Airforced through the tube 10 strikes the solid walls of chamber 11 and isdeflected therefrom through the screen wall 12 facing the threadlineagainst the threadline. Air is supplied to the tube 10 at 1.8 cubic feetper minute. The as-spun yarn wound up on the package '7 has a totaldenier of 1409, an orientation angle of 22, gamma orientation, and agamma intensity ratio of 1.5.

Physical properties of a sample of this as-spun yarn without furthertreatment are measured and set forth as item IA, Table I. The yarn hasnot been given a heat treatment and, as a consequence, the angle oforientation is not heat-stable. A second sample of this yarn is skeinedand treated in an air oven for 10 minutes at C. After this hotrelaxation step the fibers have a heat-stable orientation angle of 20,gamma orientation and a gamma intensity ratio of 3.1. This is an exampleof the preferred form of this invention and its physical properties arereported as item IB, Table I. The initial modulus (Mi), tenacity, andelongation are all given for one stress-strain test from zero elongationto the break for each sample. FIG. 3 of the drawings shows thestressstrain curves for samples IA and IB. Sample IA had a CR of 7.2while IB had a CR of 9.1.

Items IA and IB are identical except that IE was heat relaxed. Table Ishows that both samples have quite similar properties except for tensilerecovery. IB has an excellent TR of 92% while IA has a very poor T12 6EXAMPLE 11 This example illustrates the effect of drawing the fiber.

So far as favorable elastic behavior in the preferred f It is Surprisingthat the heat relaxation p range of 85% tensile recovery and up isconcerned, it applied to this yarn could so drastically alter thetensile i r f r d not t dr th fiber at all. However, some recoveryproperty. drawing is permissible but with too high a draw ratio,

The same P y as above is extruded through a p fibers having gammaorientation and the exceptional neret having 3 orifices 0f O-OZQiIIChdiameter, quenched tensile recovery of the fibers of this invention arenot as above With 1 cubic feet P minute of .Weuhd P obtained. A drawratio up to 2.5 X can be tolerated but at 525 Y-P- and then hot felaXedas above- The Y is not preferred. The procedure of Example I is rehadgamma orientation, a heat-stable orientation angle t d ith th yarn b i fd d b the feed roll of and p y properties as wn in i IQ of at 45 y.p.m.and the draw rolls run at higher speeds to Table I. ThiS iS a preferredspecific embodiment of the give the various draw ratios mentioned below.invention and possess excellent (94%) tensile recovery R f i t T bl 1,it HA i a fiber drawn 2 X after elongation, seeehd Cycle in roomtemperature air; item IIB is a fiber drawn 4 X In this Example none ofthe fibers has been drawn, over a metal pin (not shown in FIG. 1) 1 inchin diamthe spinning conditions efiecting the orientation. Item IA eter t100 C, 360 wrap) placed between the vividly illustrates that merelyhaving an orientation angle f d 11 3 d 4 d h d 11 5 d 6; d it thedefined not give the fiber of is a fiber drawn 5 X ver a metal at 60 cinvention; it must be heat-stable to get the high tensile Each fib isrelaxed?) by heating at 135 f 10 recovery Combined With the other highlevel Physical minutes in a tensionless condition and the physicalpropproperties which characterize these fibers. erties are thendetermined A peculiar characteristic of the behavior of the elastic ItemHA is a fiber within the present invention but it polypropylenes of thisinvention is illustrated in FIG. 4 25 represents a nompreferredembodiment and as Shown shovmg two Stress-Sham h Sample used to in TableI, has a TR of 82%, the lower limit on tensile Obtain these.curv.es i ii as IB above and recovery for fibers of this invention. But as the drawwas supstantlauy ldentlcal Wlth The iample Was elonratio is increased,without change in other essential congated 1n the first cycle to 50%elongatlon and then 211- lowed to recover under standard conditions Itwas then moms the fiber does not have.g.amma oneniatlon. and

the TR drops well below the minimum 82%- note items reclamped 1n thetestlng apparatus for the second cycle HB 3 T b1 I Th h I and elongatedout to the break. As FIG. 4 shows, on the an a e t e mfwentwna Practlcefirst Cycle the fiber Showed a CR of 5.6 as against the of drawlng toincrease tenaclty and MI, must be carefully appreciably higher CR of13.3 for the second cycle. On restricted to g the fibers thls lnventlonthe third and subsequent cycles the fiber behaved as in F 3 13 shown aportlon of the stress'stram CHI-Yes the second cycle. On boiling in arelaxed condition in for ltems HE and has a CR of Whlle Water the fiberreverts to a form which gives the first the curves for the other twolndlcate very low CRs for cycle behavior for the first time andthereafter goes to both- The contrast 9 the curves for Items HB and nothe second cycle type of behavior. This behavior is as Compared to HA Isy markedcharacteristic to a greater or lesser degree of the polypro- 406 is a graphic representation of an Y pylenes of this invention and isthe reason for giving TR tiOIl photograph Of a substantial duplicate Offiber IIB. values based on thesecond cycle. Other polypropylenes Itshows no apparent gamma orientation and has 9. outside of this inventionmay behave similarly. gamma intensity ratio of only 0.02. On the otherhand,

' Table I Orientation Physical Properties Item Total Draw Hot RatioRelaxation Tenacity Elongation Angle Type TR25, Percent g.p.d. 22%9122231? Ml, g.p d D.p.f.

For example, Table I gives TR values of 57% and 92% for items IA and IB,respectively; these are based on second cycle measurements. However,based on first cycle measurements, items IA and 13 show TR values of and90% respectively. Third and following cycle measurements conform withthe second cycle measurements.

FIG. 5 is a graphic representation of an X-ray diffraction photograph ofthe fiber whose stress-strain curves are shown in FIG. 4. This clearlyshows gamma orientation and is typical of the polypropylenes of whichthe fibers of the present invention are composed.

fiber IIA shows gamma orientation and a gamma intensity ratio of 1.6.

EXAMPLE III The procedure of Example I is followed with the substitutionof a spinneret containing one 0.030 inch diameter orifice, a quenchintensity of 1.9 cubic feet per minute, and the use of the same speedson all'four rolls to give a windup speed of the as-spun yarn of 216y.p.m. The as-spun monofilament (item IIIA, Table I) has a denier perfilament of 108 and an as-spun orientation angle of about (indicating analmost completely unoriented structure). However, it has potential gammaorientation.

A portion of the stress-strain curve of the above yarn is shown in FIG.3 as item IIIA. It has a compliance 8 EXAMPLE v This example illustratesthe preparation of five fibers, items V-A to V- E, Table III, allexemplifying preferred embodiments of this invention. These fibers haveexratio of Outside the range for fibers i this invention 5 cellenttensile recoveries of at least 85 gamma orienta- After above asfspun yam1S i l the draw tion, and heat stable orientation angles from 10 to 21.rolls are ad usted to give a 2 draw in an and the yarn The fibers ofthis example are not drawn deislgnated Item Table is q i g 0 Variouspolypropylenes are spun using the apparatus thls yam are then drawn m igg y g fis of Example I with the feed and draw rolls adjusted so drawsof 3 4 5 X l X to yle t 10 that no drawing is performed and an undrawnyarn is respectlvely' X'ray dlflramop p O obtained. All preparations aremade with a spinneret grap of Items Inc to IHF h no gamma Orientationhaving 34 holes of 0.012 inch in diameter similar to the Amicrophotometer trace of ltems IIIC and IIID gives spinneret of ExampleI except item V c for which is gamma mtenslty ratios of ol-lly andrespectively used a spinneret containing holes of 0.014 inch in di- Noneof these samples, items IIIB to IIIF, as drawn, 15 ameter plawd on a 1inch diamater circle shows a TR as much as A portion of each sample Thep y Of Example I is used for items and is skeined and heat relaxed at135 C. for 10 minutes V B For item a p yp py of melt index 15 to givereported m Table} HIE is made by heating the polymer of Example I in ascrew a fiber within this invention and shows a fairly good TR extruderat 230 C in the presence of tdbutyl y p of 86%. None of the items 1110to IIIF are within the '20 Oxide and then adding 1% f 4 4'- b'utylidenebiS(6-t invention although heat relaxation does effect noticeable butylm cresol) as a Stabilizer. improvement tenslle recovery as Table I w?The polymer of Example I is repeatedly extracted with Howevfirieven HemInc has a T Well below the boiling commercial grade n-heptane untilapproximately mum hmlt of Actually Item Inc takes Penna 8% of its weighthad been extracted. The residue is nent set on 25 elongation of over 72%greater than the 25 used to prepare item IIIB fiber, a strikingillustration of the loss of elastic A crystalline polyppopylene of meltindex Q18 behavior by drawing the filament 3 X as against 2 X. con, mad6by Enjay Co" of 15 51st St, New

Item IIIB tfiber has a compliance ratio between the York, NY, i d toprepare i E limits 2 and 15 and a stress at 5% elongation between the 30Ph i l properties of h as spun fib aft r m limit 0.1 and 0. 8 g.p.d.laxin'g at 135 C. for 10 minutes are given in Table III.

Table III Spinning Conditions Physical Properties Item OrientationElongation Spinneret Quench, Windup, TRQE, Tenacity, at break, Mi,g.p.d. D.p.f. Temp., C. c.f.m. y.p.m. percent gpd. percent Angle Type290 3. 6 100 1 Gamma-" 93 1. 6 430 10 12 a; 2-1 W a 3% 3 290 3: 6 93 1:7 342 12. 3 12'. 5 290 2. 6 1. 9 190 11.3 8.2 295 1. 6 74 1. 2 497 10. 016. 6 295 3. 6 s9 1. 6 520 9. 7 18.5 295 6. 0 93 1. 6 414 10.3 18.0 2902. 0 77 1. 2 477 9. 3 13. 3 290 6. 0 s4 1. 6 469 9. 3 13. 0 260 6. 092 1. 6 417 11.3 10.7 250 3. 6 1. 8 312 12. 7 4.1 230 3. 6 85 2. 0 24313. 0 3. 3 280 4.4 245 1021 do 90 300 3.2 123 Nor1nal 55 1.0 509 4.7 7 4*These fibers all have compliance ratios between 2 and 15 and showstresses at 5% elongation of between 0.1 and 0.8 gpd.

EXAMPLE IV This example illustrates not only that heat relaxation isrequired to obtain the fibers of this invention but it must beappreciable to get a heat-stable orientation angle and a TR within therange of this invention. Further, too drastic .a heat relaxation (150 C.in Table II) can also be harmful.

Skeins of item IIIB of Example III (the drawn fiber before any heattreatment) are heated for ten minutes in an air oven in a tensionlessstate at various temperatures. The tensile recoveries from 25%elongation (TR on the second cycle are given below in Table II.

Table 11 Temperature of treatment C.: TR 42 58.2

EXAMPLE VI This example illustrates the preparation of ten fibers, itemsVI-F to VI-O, Table III, using different spinning variables to show theeffect on the properties of the fibers produced. In all instances, thepolypropylene .of Example I is extruded as a melt at 289 C. using theapparatus of FIG. 1 with the feed and draw rolls adjusted so that nodrawing is performed and an undrawn yarn is obtained. The resultingfibers are allsubjected to identical heat relaxation, i.e., 10 minutesin a 135 C.

oven in a 'tensionless condition.

Fibers VII, VI-] and VIK are all prepared as above except the spinnerethas 40 holes of 0.009 inch diameter in a pattern similar to that of thespinneret used in Example I and the top of the quenching chamber 111(FIG. 2) is located one inch below the level of the face of thespinneret 9. However, the air supply and spinneret temperatures arevaried as shown in Table III. The location of the quenching chamberdelays the cooling of the fiber to a certain extent and fiber VII fallswell outside this invention. Even using the same rate of air supply (6.0cubic feet per minute) that gave the optimum VIH fiber, only a fiber(VI-J) in the non-preferred area of this invention is obtained. It wasnecessary to lower the spinneret temperature to 260 C. in order to get afiber (VIK) approaching fiber VIH in desirable elasticity.

The effect of windup speed alone is illustrated by fibers VIL and VI-Mspun from a spinneret having 34 holes (0.012 inch in diameter) arrangedin in-line rows with the quenching chamber used as shown in FIG. 1. Thefaster windup speed used in spinning [fiber VI-M cools the threadlinetoo rapidly and, as a result, the TR drops to 85% from the 90% of fiberVIL. Both fibers, however, are well within this invention.

Fibers VIN and VIO illustrate the effect of a combination of spinningvariables. They are spun in the same manner as fiber VIL except for thespinning conditions set forth in Table III. Whereas fiber VIN is apreferred specific embodiment of the invention, fiber VI-O which uses ahigher spinneret temperature, a lower quench intensity, and a lowerspinning speed, all conditions tending to increase the cooling time, isfar outside the invention with a TR of only 55%. It does not have gammaorientation.

EXAMPLE VII Using a spinneret having 3 holes (0.030 inch in diameter),yarn is spun according to the procedure of Example I but using an airfeed rate of 0.9 cubic feet per minute in the quench and with thefeedrolls 3 and 4 running at a speed of 189 y.p.m. and the draw rolls 5and 6 at a speed of 264 y.p.m. The three drawn filaments thus producedare separated and wound on to separate packages. One of these packagesof yarn is used in this example. It is heated for 30 minutes at 130 C.,the yarn being under tension since it was in package form. This effectsthe so-called heat relaxation although it is usually preferred to heatthe yarn in a tensionless condition and let it shrink as much as itwill. However, in the present example, it was desirable to leave someshrinkage in the yarn.

The yarn is then coned by conventional means and knitted into hose on a400-needle single feed seamless knitting maching using 44 courses perinch. Commercial 66 nylon yarn is used for welt, heel and toe sections.Normal 66 nylon knitting conditions are used except for a lower feedtension of 0.5 gram. The knit hose is boarded on a conventional metalform for 15 minutes in 150 C. air with a resulting 14% shrinkage. Afterboarding, the hose are scoured at 90 C., rinsed and dried. The hose thusformed have a good appearance and are notably superior instretchability, indicated by high tongue stretch values, -to both hoseknitted from normal polypropylene yarnor 66 nylon yarn. They resistbagging as well as 66 nylon hose and are much more resistant than normalpolypropylene hose.

In the following Table IV, yarn samples are removed from the hose todetermine tenacity and elongation while the tongue stretch is determinedon the hose as explained below.

The polypropylene yarn removed from the finished hose made as above hasgamma orientation, a heat-stable orientation angle of 1030, and a TR of82%. Thus it is a fiber within the present invention.

The tongue stretch values given in Table IV are determined by measuringthe inside diameter of the hose at the knee shape section under nostress (D under a stress of 7 grams (D and under a stress of 101 grams(D The stress is applied on the inside of the hose by 1 inch squareplates pivotally mounted on the ends of 2 rods which rods are pivotallyconnected near their mid points.

Tongue stretch:- X

It will be understood that the above examples are merely illustrativeand the present invention broadly comprises a fiber of polypropylenehaving gamma orientation and a heat-stable orientation angle of 10 to30.

The preparation and description of numerous fibers not falling withinthe invention have been given in the examples, the purpose being toilustrate the effect of changing various process conditions. Thesefibers not falling within the invention are not necessarily prior artfibers. So far as known, the single closest prior art is believed to beAustralian application 36,834, Example 2. This Example 2 draws thepolypropylene yarn 3.5 X too great to obtain the fiber of this inventioneven if other conditions were set in the light of the teaching herein.Actually, this Example 2 is so lacking in specificity of conditions thatfibers of all sorts of properties could be obtained by varyingcon-ditions not specified. The example states the yarn produced is verybulky which is certainly not true of the yarns whose production isdescribed in the examples herein. It would require further processchanges to make the fibers of the instant examples bulky.

As previously noted, FIG. 5 is a graphic representation of an X-raydiflraction photograph of polypropylene fiber having gamma orientationand being within the present invention; FIG. 6 is a similarrepresentation of a polypropylene fiber which is outside of theinvention and has normal rather than gamma orientation.

The diffractions 21 located on the circle 22 (20: l4.0) at an azimuthalangle greater than 50 from the equator 23 in FIG. 5 are characteristicof gamma orientation. No such diffraction is observed on the circle 22of FIG. 6. The portion of the diffraction 24 that is centered on circle25 (26=16.7) determines the orientation angle of the fiber. The highercrystallite orientation angle of FIG. 5 (16) as compared to FIG. 6 (13)is apparent. The diifractions 26 are typical of all orientedpolypropylene fiber but are not pertinent here. The diffractions 27 arelocated on a cycle 28 (20:28.6") and are used in the determination ofgamma intensity ratio. It should be noted that the pattern issymmetrically divided by the equator. The meridian is located at rightangles to the equator through the center of the pattern.

To those skilled in the art, the difference in the diffraction patternsof FIGS. 5 and 6 is striking and significant. The diifractions 21 ofFIG. 5 are unusual and immediately reflect the unique crystallinestructure of the polypropylene fibers of the present invention.

The elastomeric fibers of the present invention have an extremelyfavorable combination of properties, featured by an elasticityheretofore unknown in polypropylene fibers. Example VII shows the use offibers of the invention in hosiery. These fibers are quite advantageousfor use in such applications as automobile upholstery, seatcovers, andthe like because such fabrics and material possess unusually good formrecovery. The use of fibers of this invention in non-Woven fabric islikewise advantageous because they impart such good form recovery.

As many apparently widely different embodiments of this invention may bemade without departing from the spirit and scope thereof, it is to beunderstood that the invention is not limited to the specific embodimentsthereof except as defined in the appended claims.

The invention claimed is:

1. An elastomeric fiber of highly crystalline polypropylenecharacterized by melt index of from 0.1 to 200, said fiber having anelongation at break of from 100% to 700%, gamma orientation, a heatstable orientation angle of 10 to 30, and a tensile recovery on thesecond and succeeding stretch cycles from a 25% elongation of at least82%, said tensile recovery having been achieved by a separate heattreatment of the fiber, after it has 12 been spun, at an elevatedtemperature of from 105 C. to 160 C.

2. The fiber of claim 1 having a gamma intensity of 'at least 1.0 and aheat-stable orientation angle of 10 to 3. The fiber of claim 1 having atensile recovery on the second and succeeding stretch cycles from a 25%elongation of at least 90%.

4. The fibers of claim 1 in the form of a non-woven fabric.

References Cited by the Examiner UNITED STATES PATENTS 3,019,507 2/1962Maraglia-no et al. 2872 FOREIGN PATENTS 223,630 1/ 1958 Australia.

JOSEPH L. SCHOFER, Primary Examiner.

ROSCOE V. PARKER, ]R., A. J. SMEDEROVAC,

E. M. OLSTEIN, M. B. KURTZMAN, Examiners.

1. AN ELASTOMERIC FIBER OF HIGHLY CRYSTALLINE POLYPROPYLENECHARACTERIZED BY MELT INDEX OF FROM 0.1 TO 200, SAID FIBER HAVING ANELONGATION AT BREAK OF FROM 100% TO 700%, GAMMA ORIENTATION, A HEATSTABLE ORIENTATION ANGLE OF 10* TO 30*, AND A TENSILE RECOVERY ON THESECOND AND SUCCEEDING STRETCH CYCLES FROM A 25% ELONGATION OF AT LEAST82%, SAID TENSILE RECOVERY HAVING BEEN ACHIEVED BY A SEPARATE HEATTREATMENT OF THE FIBER, AFTER IT HAS BEEN SPUN, AT AN ELEVATEDTEMPERATURE OF FROM 105*C. TO 160*C.